Top five of the UK marine species affected by climate change

Atlantic cod

The Atlantic cod favours cool waters and is found all around the UK coast and throughout the North Atlantic. Highly valued as a food resource, it has been fished extensively throughout UK waters, resulting in a severe decline in numbers over the past century. Irish Seas stocks are “seriously depleted” and west Scotland stocks are “seriously over-fished”, while North Sea populations, and stocks to the west of Britain and south of Ireland, are also “outside safe biological limits”.

While over-fishing has been identified as the greatest cause of population decline of the Atlantic cod, the species is also sensitive to temperature variation – studies suggest that the ability of stocks to adapt to temperature change is limited. Further warming of our seas, caused by climate change, may force southern cod stocks northwards, squeezing the range of northern populations resulting in an overall reduced population size. Changes in planktonic activity as a result of climate change may also impact populations because the availability of food for larval cod at the time of hatching is affected.

Calanus zooplankton

Calanus is a group of marine shrimp-like copepods which form the most abundant zooplankton species in the North East Atlantic. The effect of sea surface temperature rise is considered the most important characteristic affecting plankton productivity and distribution and has changed so dramatically that it is referred to as a regime shift in the NE Atlantic. There has been an overall long-term downward trend in copepod abundance in many areas, which is believed to be climatically induced. The overall abundance of Calanus has reduced by 60% since the 1940s. Furthermore, the ratio of the cold-temperature C. finmarchicus to the warm- temperature C. helgolandicus is a useful indicator of the warming trend in the North Sea, with the latter becoming dominant over the past decade.

These changes have important implications for many other species (notably the Atlantic cod and sandeels) in terms of food availability given that all other parts of the ecosystem ultimately rely upon them.

Pacific wire weed

Warming waters as a result of climate change favour a number of non-native species. These species are therefore more likely to extend their distributions and become established following introduction.

For example, wire weed – a large brown seaweed that is native to the waters around Japan – is now widespread and it is believed that the spread of this species throughout UK waters is inevitable.

It was introduced with commercial oysters to France and has subsequently spread to Britain. It is one of more than 50 alien species which have invaded UK waters, many of which pose a threat to native species. In UK waters wire weed can grow up to 12 times bigger than normal and is known to compete with native, some of which are protected, species such as eelgrass.

It can grow in a variety of habitats because it is tolerant of large environmental fluctuations and can even thrive in estuarine conditions. It establishes itself on hard substrata in shallow waters and grows upwards to form large floating masses, which can block out sunlight, slow down the flow of water, increase sedimentation and reduce the nutrients available to other species.

Kittiwake

An increasing number of studies have shown climate effects on UK seabird populations and some worrying changes in UK seabirds have been witnessed over recent years. For instance, populations of black-legged kittiwakes have declined by more than 50% in the North Sea since 1990. Climate change is likely to have contributed to these problems as several studies have shown that warm winters are bad for seabirds – both breeding success and individual survival of black-legged kittiwakes was found to be lower following warm winters. It is believed that this happens because warm sea temperatures impact upon the availability of sandeels – which form a major part of their diet – resulting in a reduction of the seabirds’ food supply. Seabirds such as kittiwakes are particularly dependent upon sandeels in the breeding season for feeding their young. Breeding failure in many seabird species has been linked to a chronic shortage of food and, in particular, key fish stocks such as sandeel.

Sandeel

Sandeels are small eel-like fish which spend most of their life buried in the sand. They are an important component of food webs in the North Atlantic, being important prey species for many marine predators. Sandeel populations are currently in decline and there has been a correlation between poor recruitment to sandeel stocks and periods of positive North Atlantic oscillation (ie warm spells in winter). The decline in sandeel stocks has been proposed as an explanation for the widespread failure of many seabird colonies in recent breeding seasons.

It appears that climate change has played a significant part in sandeel declines. Sea surface temperatures in the North Sea in recent years have been significantly higher than the 30-year average. A study of sandeels in the North Sea indicates that their numbers are lower in years which are warmer during the eggs and larval stages and there is further evidence that this is, in turn, linked to plankton abundance around the time of sandeel egg hatching. The study also indicated that the adverse effect of rising sea temperatures is most marked in the southern North Sea where the lesser sandeel is near the southern limit of its range. The southern limit of sandeel distribution may shift northwards if conditions continue to get warmer.

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